See if you can download a program such as HWMonitor or Everest Ultimate and check what your CPU voltage is....I'm assuming here there is a bit of a Vdroop so you should be fine at maybe 1.28V...Let us know what the voltage is. I have a feeling you actually should be able to go to 4.0GHz on this voltage!

__________________Hardcore Folding at it's BEST! HWC - TPU.... There can be only one team in front! TPU, can you smell our *sses already?